Automatic Dependent Surveillance (ADS), a new standard adopted by many aviation authorities worldwide offers a great leap forward in aircraft surveillance capabilities. More information is made available than before with conventional primary and secondary radar technologies, and as ADS-B does not require major conventional radar ground infrastructure, the cost of implementation is far lower than Prior Art techniques.
Whether ADS will allow the decommissioning of primary conventional radars is the subject of many ongoing debates. However, most nations see the benefits in the implementation of a relatively low cost flight tracking technology. Countries with vast tracts of land or mountainous terrain that is not viable for conventional radar see the technology as highly cost beneficial.
Countries ranging from Australia to Taiwan have adopted ADS-B technology. Many working groups consisting of members of the international aviation community have participated in the development of many aircraft avionics and ground systems standards, for example RTCA Special Committee 186, which developed the ADS-B MASPS. A selection of some of the Committee's issue papers are listed below, and incorporated herein by reference. Additional papers, on the subject are available from http://adsb.tc.faa.gov/RFG.htm, also incorporated herein by reference.
The aforementioned Issue Papers, all of which are incorporated here by reference:
File Name (*.PDF)SizeDateStatusDescriptionASA-ASAS-Issue-1.5 mNov. 23, 2004—ZIP file containing all submitted issuePapers.zippapers (1–20)Blank ASAS Issue8 k——Blank submission formPaper.zipIP01 TCAS ASA14 kApr. 23, 2003WithdrawnTCAS Platform UsageMASPS IssueIP02 Degraded Target16 kApr. 23, 2003ClosedDegraded Target Utility IndicatorUtility IndicatorIP03 ASSAP19 kApr. 23, 2003ClosedSpecifications are needed for ASSAPOwnship Dataprocessing of Ownship data andProcessinginterfaces from ASSAP to the ADS-Btransmitting subsystemIP04 Unknown SIL15 kApr. 23, 2003OpenLegacy GPS Systems are unable toprovide values for SILIP05 Application38 kApr. 23, 2003DeferredRecommendations for changing theNames and Acronymsnaming and acronym conventions forAirborne Surveillance Applications.IP06 Minimum Data17 kApr. 23, 2003ClosedCautions against placing minimumQuality Requirementsoutput requirements on ADS-B data.IP07 Enhanced SIL21 kApr. 23, 2003ClosedRequests that SIL definitions beBit Definitionsextended to include intermediate valuesthan those specified in DO-242A.IP08 CDTI - Ownship59 kApr. 23, 2003OpenProposal to address CDTI displayDirectionalityrequirements when ownship loses itsdirectionality information.IP09 CDTI - Display54 kApr. 23, 2003OpenProposal for how CDTI symbologyof Positionmight represent position uncertainty.UncertaintyIP10 CDTI - Altitude15 kJun. 18, 2003OpenRequests clarification on best choice ofUsagealtitude source (i.e. baro vs. geo) fordetermining relative and absolutealtitude of displayed CDTI traffic.IP11 ASA - 64 kJan. 13, 2004PendingIdentification of an inconsistency ofContinuity in Tablescontinuity requirements between Tables2–3 & 3–12–3 and 3–1 in ASA MASPS.IP12 ASA - Air-66 kJan. 13, 2004PendingProblems with ASA MASPS air/GroundGrounddetermination when A/V has noDeterminationautomatic detection means.IP13 ASSAP - TIS-B58 kFeb. 13, 2004PendingRequest to coordinate with WG2 that theRegistrationTIS-B MASPS requires the appropriateregistration functions between ADS-Band ground sensors such as SSR.IP14 STP - Velocity64 kSep. 10, 2004PendingProposal for new ADS-B field to conveyLag Indicatorvelocity tracker lag.IP15 ASA - ADS-B66 kSep. 10, 2004PendingQuestion as to whether there needs to beOUT Power Switcha requirement for ADS-B Out systems tohave an ON/OFF switch available to thepilotIP16 ASA - Surface58 kSep. 01, 2004PendingProblem of Surface Vehicles whichVehicles in Tunnelsoperate on in tunnels under runways andtaxiways. How do Aircraft track thesevehicles without placing them on therunways or taxiways?IP17 CDTI - ADS-B25 kNov. 03, 2004OpenSummation of issue of whether or notTCAS SymbolCDTI should introduce directionalityDirectionalityindication onto TCAS targets.IP18 CDTI - Velocity718 kNov. 03, 2004OpenSummation of issues related to usingVector Issuesvelocity vectors for CDTI targets.IP19 ASSAP -17 kNov. 02, 2004PendingSince there is no means on the receiveReceived NUC meansside to determine if transmitting DO-260Integrity unknowncompliant systems are also TSO C166compliant, integrity must be assumed tobe ZERO for received data.IP20 ASSAP - Limit18 kNov. 02, 2004PendingNIC & NAC values of 9 or greater areof NIC & NAC to 8defined with vertical considerations.or lessSince initial STP MOPS will not addressthese factors, ASSAP must not usevalues greater than 8 for these fields.
The FAA has also successfully used ADS-B in a program called CAPSTONE, (See, http://www.alaska.faa.gov/capstone/, incorporated herein by reference). The Taiwan CAA started a combined ADS-B and multilateration program in the past few years as detailed on the website: http://www.caa.gov.tw/files/org/CNS_ATMSite/Surveillance.htm, also incorporated herein by reference.
The Taiwan CAA website contains a good description of ADS-C. The website explains that in order to meet the ADS operational requirements, the following four types of contract are supported. The first is the Demand contract 150, in which an aircraft provides data immediately and only once illustrated in FIG. 1, (ADS-C demand contract model). Referring to FIG. 1, control center 140 may send a request 110 for a transmission to aircraft 120. This request 110 may include a transmission number and transmission time (current time). The request is generally sent once only. In response to the request 110, aircraft 120 sends a message transmission 130 which may include aircraft identification and location data and an end of transmission signal. The control center 140 may then use this information to update aircraft position information on a control screen or the like, or for other purposes.
The second type of contract is the Periodic contract 250, in which an aircraft provides data periodically as shown in FIG. 2 (ADS-C periodic contract model). Referring to FIG. 2, control center 240 may send a request 210, which includes a transmission interval of X minutes, to aircraft 220. Aircraft 220 then sends a reply transmission 232 and then after the X minute (or other time interval) a second transmission 234, and a third transmission 236, and so forth. Each transmission 232, 234, 236, et al. may include aircraft identification and position information as well as other aircraft information. The control center 240 may then use this information to update aircraft position information on a control screen or the like, or for other purposes.
The third type of contract is the Event contract, in which an aircraft provides information when certain events are detected by aircraft avionics as shown in FIG. 3 (ADS-C event contract model). In the Event contract, a transmission may be generated by the aircraft whenever one or more events occurs. Examples of such events may include a way point change 310, in which the aircraft passes through a waypoint and/or heads toward another waypoint on an airchart. Another event example may include a speed change 320 in which the aircraft velocity changes (in this example from mach 0.82 to Mach 0.78). A third example is an altitude change, in which an aircraft changes from a particular latitude or from an assigned altitude. A fourth example is a heading/track change, in which an aircraft changes from a particular heading or predetermined track. These four examples of events are not inclusive, and other events may be used to trigger event reporting.
The fourth type of contract is the Emergency contract, in which an aircraft provides data, in the case of an emergency. In this type of contract, a transmission is generated if one or more emergency conditions are triggered, including automatically determined emergency conditions (loss of cabin pressure, engine out, or the like) and pilot indicated emergencies.
With ADS-B, the aircraft transmits aircraft parameters derived from an on-board navigation system via a broadcast data link to other aircraft or the ground control stations, and can be used to monitor the airport surface status as illustrated in FIG. 4 (ADS-B application). Referring to FIG. 4, aircraft 420 may derive position information from signals received from (for example) global positioning system satellite 460. When interrogated by air traffic radar 445 or in response to other indicia, aircraft 420 may emit transponder data (e.g., identification and/or altitude data and/or other data), which may be received by radar 445 such that Air Traffic Management center 440 may track the aircraft.
In addition, aircraft 420 may emit an ADS-B signal, which may be received by antenna 470 and/or other aircraft 425. ADS-B data may include information as to aircraft position and altitude, aircraft identification, and other data. This data may be used to identify and track aircraft and also provide other features, such as collision avoidance.
ADS-B signals may also be multilaterated by measuring the time difference of arrival (TDOA) at multiple antenna sites 470 to indicate aircraft position. The assignee of the present application has developed a number of techniques for implementing such multilateration, as described in the various Patents and applications previously incorporated by reference.
Other aviation authorities have also embraced the use of wide area multilateration coupled with ADS-B, including Austrocontrol as discussed in Aviation Week and Space Technology, Mar. 7, 2005, page 44-45, incorporated herein by reference. Some detractors of the technology have raised security concerns, such as Darryl Phillips, who wrote and distributed ADS-B, Automatic Dependent Surveillance—Broadcast Will ADS-B Increase Safety and Security for Aviation? first written in March 1999, revised July 2000 , by Darryl H. Phillips, AirSport Corporation, 1100 West Cherokee, Sallisaw Okla. 74955. See, http://www.airsport-corp.com/adsb2.htm, also incorporated herein by reference.
Other companies have also raised some security concerns and have come up with various solutions including secure communications links. See, for example Published U.S. Patent Application Publication No. 20040086121, entitled Secure Automatic Dependent Surveillance, also incorporated herein by reference. Others have attempted to develop methods to fuse data from disparate sources, attempting to build high confidence or “robust” data fusion processes, as illustrated for example in Published U.S. Patent Application Publication No. 20040130479, also incorporated herein by reference.
Another security concern is the prevention of a pilot (or terrorist) turning off the ADS-B transponder, as was the case with the hijacked aircraft on Sep. 11, 2001. This has lead to many methods such as Published U.S. Patent Application Publication Nos. 20040148067 and 20030060941, entitled Uninterruptible ADS-B System for Aircraft Tracking, both of which are incorporated herein by reference.
U.S. Pat. App 20030193409 describes a method and apparatus for tracking aircraft and securing against unauthorized access. This approach uses the aircraft's derived surveillance information in conjunction with GIS data to determine if an aircraft is off course. Other methods include building confidence levels in target positions using correlation techniques, such as that described in Published U.S. patent application No. 20030154018, entitled Multi-source target correlation, incorporated herein by reference.
As noted in the references cited above, the threat of ADS-B spoofing is of concern to many parties. Altering the existing ADS-B infrastructure to prevent such spoofing would require extensive investment in revising existing infrastructure and also changing out ADS-B equipment in existing aircraft. Such a radical overhaul of the ADS-B system is not cost-effective or practical. A technique for detecting ADS-B spoofing which is independent of ADS-B systems is required.
The assignee of the present application has developed an array of equipment and software and systems for tracking and identifying aircraft based upon multilateration—using aircraft radio signals to detect position and identification of an aircraft. As multilateration moved from an airport-based system to off airport applications such as wide area it became necessary to find sites off-airport to place the sensors. Off airport sites needed to have power, telecommunication, security and the ability to position antennas at reasonable heights to overcome obstructions to achieve line of site to aircraft.
In some of the earlier sites, such as T.F. Green airport in Providence, R.I. and Hyannis Airport in Barnstable, Mass., off airport sites included tops of various buildings, and Government owned communication towers. Because of the nature of the equipment at that time including the frequency use and large physical size and architecture it was not thought practical that commercial cell phone towers could be used.